Topshop, which is owned by multinational Arcadia Group, responded to the criticism on Thursday in a statement that was posted to website Buzzfeed.

The statement said: "Topshop has long made it a priority to showcase a healthy size image to its customer," adding "Mannequins are made from solid fibreglass, so in order for clothing to fit, the form of the mannequins needs to be of certain dimensions to allow clothing to be put on and removed; this is therefore not meant to be a representation of the average female body."

The use of unrealistically thin mannequins was last in focus in the U.K. last November, when one of the country's large department store chains, Debenhams, introduced a selection of "plus-sized" mannequins. It said the move was aimed at combating poor body image among women.

The move was a canny one, according to Isabel Cavill, an apparel and luxury analyst at Planet Retail. She told CNBC last November that "recognizing that women's average size has increased is a clever move. Shops that still use size 10 mannequins – such as Marks and Spencer – are not reflecting the real market."